The present invention relates to an apparatus for detecting an abnormality occurring in a rotational speed sensor, and is applicable particularly, but not exclusively, to an anti-skid control system.
Generally, anti-skid control systems for use in a vehicle to control the braking hydraulic pressure on the basis of a detection signal obtained by a wheel speed sensor, with a view to maximizing the braking efficiency.
Since failures of the wheel speed sensor result in difficulty in maintaining the appropriate anti-skid control operation, the execution of a fail-safe control would be required in response to the failures because of the necessity to ensure the vehicle braking operation. Therefore, various systems have hitherto been proposed for the detection of abnormality of the wheel speed sensor. One example of such systems is disclosed in Japanese Patent Provisional Publication No. 58-61052, the technique of which involves differentiating the detection signal from the wheel speed sensor and detecting a temporarily occurring abnormality by comparing the differentiated value with a reference value.
However, such a prior art system would suffer the problems in that the circuit arrangement is complex because the detection signal from the wheel speed sensor is differentiated after converted into an analog signal and difficulty is encountered to quickly detect the abnormality because of the requirement of considerable processing time.